This invention relates to electronic parts and multilayer circuits using prepreg and substrate, and more particularly, to such electronic parts suitable for operation in a high frequency region of at least 100 MHz and for use in magnetic characteristics-utilizing applications and magnetic shields.
In the field of electronic equipment for communication, commercial and industrial applications, the current mounting technology seeks further miniaturization and higher density packaging. Concomitant with this trend, materials are required to have better heat resistance, dimensional stability, electrical characteristics and moldability.
Known electronic parts or multilayer substrates for high frequency operation include sintered ferrite and sintered ceramics which are laminated and molded into substrate form. Laminating such materials into multilayer substrates has been practiced in the art because of the advantage of potential miniaturization.
The use of sintered ferrite and sintered ceramics, however, gives rise to several problems. A number of steps are involved in firing and thick film printing. Sintered materials suffer from inherent defects including cracks and warp caused by firing. Cracks are also induced by the differential thermal expansion between sintered material and printed circuit board. It is thus increasingly required to replace the sintered materials by resinous materials.
With resinous materials as such, however, a satisfactory dielectric constant is arrived at with great difficulty, and little improvement in magnetic permeability is achievable. Then, electronic parts utilizing resinous materials as such fail to provide satisfactory characteristics and become large in size, rendering it difficult to reduce the size and thickness of electronic parts.
It is also known from JP-A 8-69712 and JP-A 11-192620 to mix resinous materials with ceramic powder into composite materials. These composite materials, however, have unsatisfactory high-frequency characteristics and magnetic characteristics.
Also, JP-B 6-14600 discloses the sheeting technique of forming plural materials into layers, followed by lamination. This method involves a number of steps. The operating frequency of the multilayer part referred to in this patent is several megahertz at maximum. No study is made on the performance of the multilayer part in the high-frequency region of at least 100 MHz.
An object of the invention is to provide a multilayer electronic part having the advantages of small size, excellent performance and improved overall electrical characteristics, using plural layers selected from among composite resin substrates having a sufficiently high or low dielectric constant, composite resin substrates having a sufficiently high dielectric constant, and composite resin substrate layers having a sufficiently high Q value.
According to the invention, there is provided a multilayer electronic part comprising constituent layers of at least two types formed of hybrid or composite materials and a conductor layer formed on at least one composite material layer, the conductor layer constructing a predetermined electric circuit.
The multilayer electronic part is typically used in a frequency band of at least 100 MHz. Preferably the constituent layers include a layer containing at least reinforcing fibers. Also preferably, the constituent layers include at least one layer containing at least one flame retardant.
In a first preferred embodiment, the constituent layers include at least one first composite dielectric layer in which a dielectric powder having a dielectric constant (or relative permittivity) of 5 to 10,000 and a dielectric dissipation factor of 0.00002 to 0.01 is dispersed in an amount of 10 to 65% by volume such that the first composite dielectric layer has a dielectric constant of 5 to 20 and a dielectric dissipation factor of 0.0025 to 0.0075.
In a second preferred embodiment, the constituent layers include at least one second composite dielectric layer in which a dielectric powder having a dielectric constant of 20 to 20,000 and a dielectric dissipation factor of 0.01 to 0.0001 is dispersed in an amount of 10 to 65% by volume such that the second composite dielectric layer has a dielectric constant of 10 to 40 and a dielectric dissipation factor of 0.0075 to 0.025.
In a third preferred embodiment, the constituent layers include at least one composite magnetic layer in which a magnetic powder is dispersed in an amount of 10 to 65% by volume such that the composite magnetic layer has a magnetic permeability of 3 to 20.
According to the invention, multilayer substrates are constructed using a composite material of at least a resin and a magnetic powder and a composite material of at least a resin and a dielectric powder. There can be obtained magnetic substrates having a low dielectric constant and excellent high-frequency characteristics and dielectric substrates having excellent high-frequency characteristics. As a consequence, a multilayer electronic part having excellent overall high-frequency characteristics is obtainable.